The present invention relates generally to manufacturing rotor assemblies, and, more specifically, to the assembly thereof.
A gas turbine engine is an example of a large rotary machine requiring dimensional precision for reducing vibration at high rotational speed. Vibration may occur due to mass unbalance around an axial centerline axis of the engine, or due to eccentricity of the rotor therearound.
Eccentricity is a particular concern in an assembly of rotor components since the interconnecting joints therebetween may contribute to eccentricity. The individual rotors in a typical gas turbine engine vary in configuration for aerodynamic, mechanical, and aero-mechanical reasons which increases the complexity of the engine design and the difficulty in reducing undesirable eccentricity.
For example, a multistage axial compressor includes rows of decreasing size compressor blades extending radially outwardly from supporting rotor disks. The blades may be removably mounted in corresponding dovetail slots formed in the perimeter of the disks, or may be integrally formed therewith in a unitary construction known as a blisk. Individual disks may be bolted together at corresponding annular flanges having a row of axial bolt holes through which fastening bolts extend for joining together the several rotors in axial end-to-end alignment.
Some rotor disks are typically formed in groups in a common or unitary rotor drum, with the drum having end flanges bolted to adjoining rotors having similar annular flanges therefor.
Accordingly, the multistage assembled compressor rotor includes several rotor disks axially joined together at corresponding annular flanges. Each rotor is separately manufactured and is subject to eccentricity between its forward and aft mounting flanges, and is also subject to non-perpendicularity or tilt of its flanges relative to the axial centerline axis of the engine.
Both eccentricity and tilt of the rotor end flanges are random and preferably limited to relatively small values. However, the assembly of the individual rotors with their corresponding flange eccentricities and tilts is subject to stack-up and the possibility of significantly larger maximum eccentricity and tilt collectively due to the individual eccentricities and tilts.
Accordingly, when the rotor assembly is mounted in bearings in the supporting engine stator, the corresponding rotor seats or journals mounted in the bearings may have relative eccentricity and tilt therebetween, and intermediate flange joints between individual rotors of the assembly may have an eccentricity from the engine centerline axis which exceeds the specified limit on eccentricity for the rotors due to stack-up. In this case, the rotor assembly must be tom down and reassembled in an attempt to reduce stackup eccentricities and tilt to an acceptable level within specification.
One manner of reducing the random nature of the assembly stackup is to measure each rotor during the assembly sequence to determine the eccentricity and tilt between its end flanges and then assembling that component to a preceding component for reducing the collective stackup of eccentricity and tilt upon final rotor assembly.
Measurement equipment for effecting this sequential assembly process has been commercially available and used in this country for several years. Individual rotors are mounted on a turntable using a suitable fixture therefor so that the rotor may be rotated about its axial centerline axis. Linear measurement gauges are mounted to the table and engage the two corresponding mounting flanges of the rotor for measuring any variation of radius of the flanges from the axial centerline axis around the circumference of the flanges, and for measuring any variation in axial position of each of the flanges around the circumference.
The gauges are operatively joined to a digitally programmable computer controller which simultaneously receives the measurement data from the two gauges mounted at each end flange during inspection. The controller is programmed to calculate various geometric parameters for the two end flanges. In particular, the radial measurement data may be used to calculate both eccentricity and concentricity of the end flanges represented by deviation from a calculated center and a datum axis. In this way, relative eccentricity between the two end flanges may be measured and may be represented by a vector having an eccentricity magnitude and rotary or angular direction relative to a suitable reference point on the rotor.
Additionally, the controller may calculate non-perpendicularity or tilt of the end flanges relative to a datum plane or axis. In this way, relative tilt between the axial end faces of the flanges may be determined in the form of another vector having an angular tilt magnitude and angular direction relative to the rotor reference.
Since both eccentricity and tilt affect the final eccentricity of the assembled rotors, both factors are used in assembling the rotors. However, the tilt vector must be suitably transformed into a corresponding eccentricity at either one of the rotor journals being mounted in the bearings. This is readily accomplished using simple trigonometry to project the relative tilt for each of the rotor components to the same end journal axial plane for determining the corresponding projected eccentricity thereat. The measured eccentricity for each rotor may be vector summed with the projected eccentricity corresponding with the rotor tilt vector to provide a total eccentricity vector for the individual rotor having magnitude and angular direction.
During typical assembly of a multi-rotor axial compressor, each rotor is measured for eccentricity and tilt and the total eccentricity vector therefor is determined. The rotors are measured, inspected, and assembled in turn so that the total eccentricity vector for each subsequent rotor is assembled to the preceding rotor either directly in phase, or with the vectors being 180 degrees out of phase. Since the length of the vectors correspond with the individual magnitudes of eccentricity, the rotors are assembled in turn so that the corresponding vectors balance each other in addition or subtraction as required for minimizing the final eccentricity between the first rotor and the last assembled rotor.
The eccentricity and tilt of the individual rotors is thusly substantially balanced from rotor to rotor, but typically results in some remaining eccentricity between the two journal ends of the completed rotor assembly. Furthermore, the in or out of phase alignment of the eccentricity vectors is random as the adjoining rotors are interconnected, with the vectors being added or subtracted.
Accordingly, upon final inspection of the assembled rotor either the net eccentricity between the end journals or an inter-rotor eccentricity may nevertheless exceed the specified limit on eccentricity. This would then require teardown of the rotor assembly and re-assembly in an attempt to reduce net eccentricity and stage eccentricity to within acceptable limits.
Accordingly, it is desired to improve the assembly process of multiple rotors for minimizing eccentricity thereof from a common axial centerline axis.
A plurality of rotors are individually measured for determining relative eccentricity between forward and aft annular mounting ends thereof. The measured rotor eccentricities are stacked analytically to minimize eccentricity from a centerline axis. The rotors are then assembled axially end-to-end to correspond with the stacked measured eccentricities thereof.